Excess nutrients reach surface-water resources in direct discharges from point sources (for example, municipal wastewater-treatment plants) and from diffuse non—point sources (for example, nutrient runoff from farmland, urban, and suburban areas and air pollution). Because the nutrient-use efficiency of crops is less than 100%, farmers need to apply more nutrients to their fields than the plants need for healthy growth. The challenge for all farmers is to add fertilizer at the optimal time and rate and then to keep the nutrients in the field. Concomitant with the substantial increases in agronomic yields that have allowed agriculture and fish production to meet the food needs of 7 billion people has been a need for higher rates of application of fertilizers, which have exacerbated runoff, limited the effectiveness of strategies for remediating eutrophication, and resulted in production of nitrous oxide as a byproduct of nitrification and denitrification processes. (Nutrient sources for the Chesapeake Bay and the Gulf of Mexico are shown in Figure 2-1.) Addressing the nutrient loading will require increased scientific understanding, including new information on pollution sources, on emerging technologies that could be used in agriculture and in wastewater treatment, on water quality conditions, and on the response of ecosystems to increasing nutrient loads and shifting stochiometry. Such scientific understanding can be gained only through integrated research.
The Chesapeake Bay, North America’s largest estuary, offers a highly instructive example of contributions made by EPA and allied researchers to a more fundamental understanding of the physical processes that lead to the effects of nutrient pollution. Substantial reductions in nutrient discharges from sewage-treatment plants, factories, and other point sources of pollution have been achieved in the bay watershed since the 1970s but are insufficient to meet water-quality goals. The challenges faced by the Chesapeake Bay ecosystem are shared by many other ecosystems, but the differences among them make the required research and the effective tools for addressing the challenges more complex. For example, 500 km to the north of the Chesapeake Bay lies Narragansett Bay. Although smaller than its southern cousin, it shares many historical and ecologic characteristics; but the challenges faced today by the Narragansett Bay (where EPA’s Atlantic Ecology Division Laboratory is located) have developed in very different ways. The region has historically been dominated by agricultural activity, but that is no longer the case. Today, Narragansett Bay suffers from excess nitrogen inputs, largely from upstream wastewater-treatment facilities (Pryor et al. 2007). The upper reaches of the bay have been closed to shellfishing and swimming for decades. In 2004, Rhode Island mandated a minimum standard for effluent nitrogen from the wastewater facilities within its jurisdiction, yet the science suggests that without concomitant reductions in nitrogen from wastewater facilities upstream on the Blackstone River in Massachusetts and reduction in nitrogen inputs that result directly and indirectly from air pollution, restoring the waters of the upper bay will be difficult (see Figure 2-2). Narragansett Bay, as a result of the large influence of sewered effluents, should be one of the easiest places to